In exploration and production operations for natural resources such as hydrocarbon-based fluids (e.g., oil and natural gas), a wellbore may be drilled into a subterranean earth formation. If the wellbore comes into contact with a fluid reservoir, the fluid may then be extracted If the wellbore does not contact the fluid reservoir, or as the resources in a reservoir are depleted, it may be useful to create additional wellbores to access additional resources. For instance, another wellbore may be drilled to the downhole location of an additional fluid reservoir.
In some cases, however, directional drilling may be used in lieu of creating, a new, wellbore. In directional drilling, a new borehole may deviate from an existing wellbore. The new borehole may extend laterally at a desired trajectory suitable for reaching a particular downhole location. In creating the lateral borehole, a deflecting member may be employed in a method referred to as sidetracking.
An example deflection member may include a whipstock having a ramp surface that guide a milling bit. To create the lateral borehole, the whipstock or other deflection member can be set at a desired depth and the ramp surface oriented to provide a particular trajectory to facilitate a desired drill path. Often, one process is provided to deliver, secure and orient the whipstock within the existing wellbore. A second trip may then be used to deliver a bottomhole assembly having a milling bit. The milling bit can move along the ramp surface of the whipstock or other deflection member, and the ramp surface will guide the milling bit into the casing of a cased wellbore where a window can be milled in the casing. In the case of an uncased or openhole wellbore a drill bit may be moved into contact with the Wall of the wellbore. In either case, the milling bit or drill bit may then be extended into the surrounding subterranean formation and follow the desired path to reach a particular destination.